Integrated fin and strap structure for an access transistor of a trench capacitor

ABSTRACT

At least one dielectric pad layer is formed on a semiconductor-on-insulator (SOI) substrate. A deep trench is formed in the SOI substrate, and a combination of an outer electrode, a node dielectric, and an inner electrode are formed such that the top surface of the inner electrode is recessed below the top surface of a buried insulator layer of the SOI substrate. Selective epitaxy is performed to fill a cavity overlying the inner electrode with an epitaxial semiconductor material portion. A top semiconductor material layer and the epitaxial semiconductor material portion are patterned to form a fin structure including a portion of the top semiconductor material layer and a portion of the epitaxial semiconductor material portion. The epitaxial semiconductor material portion functions as a conductive strap structure between the inner electrode and a semiconductor device to be formed on the fin structure.

BACKGROUND

The present disclosure relates to a semiconductor structure, andparticularly to an epitaxial strap structure between a fin field effecttransistor (FET) and a trench capacitor, and a method of manufacturingthe same.

Deep trench capacitors are used in a variety of semiconductor chips forhigh areal capacitance and low device leakage. Typically, a deep trenchcapacitor provides a capacitance in the range from 4 fF (femto-Farad) to120 fF. A deep trench capacitor may be employed as a charge storage unitin a dynamic random access memory (DRAM), which may be provided as astand-alone semiconductor chip, or may be embedded in a system-on-chip(SoC) semiconductor chip. A deep trench capacitor may also be employedin a variety of circuit applications such as a charge pump or acapacitive analog component in a radio-frequency (RF) circuit.

As dimensions of semiconductor devices scale, providing a robust lowresistance path for electrical conduction between an inner electrode ofa transistor and the source of an access transistor becomes a challengebecause available area for forming a conductive strap structuredecreases. Conventional processes for forming a conductive strapstructure as known in the art introduces additional complexity when sucha conductive strap structure needs to be formed between the innerelectrode and a three-dimensional field effect transistor such as a finfield effect transistor (finFET).

BRIEF SUMMARY

At least one dielectric pad layer is formed on asemiconductor-on-insulator (SOI) substrate. A deep trench is formed inthe SOI substrate, and a combination of an outer electrode, a nodedielectric, and an inner electrode are formed such that the top surfaceof the inner electrode is recessed below the top surface of a buriedinsulator layer of the SOI substrate. Selective epitaxy is performed tofill a cavity overlying the inner electrode with an epitaxialsemiconductor material portion. A top semiconductor material layer andthe epitaxial semiconductor material portion are patterned to form a finstructure including a portion of the top semiconductor material layerand a portion of the epitaxial semiconductor material portion. Theepitaxial semiconductor material portion functions as a conductive strapstructure between the inner electrode and a semiconductor device to beformed on the fin structure.

According to an aspect of the present disclosure, a semiconductorstructure includes a trench capacitor embedded in a stack of asemiconductor substrate and an insulator layer. The trench capacitorincludes an inner electrode, a node dielectric, and an outer electrode.The semiconductor structure further includes an integrated fin and strapstructure located on the insulator layer. The integrated fin and strapstructure includes a semiconductor fin and an epitaxial semiconductorstrap structure. The epitaxial semiconductor strap structure isepitaxially aligned to the semiconductor fin and extends below a topsurface of the insulator layer.

According to another aspect of the present disclosure, a method offorming a semiconductor structure is provided. At least one pad layer isformed on a top semiconductor layer of a semiconductor-on-insulator(SOI) substrate. A trench extending below a bottom surface of aninsulator layer is formed within the SOI substrate. A trench capacitorincluding an inner electrode, a node dielectric, and an outer electrodeis formed in the SOI substrate. An epitaxial semiconductor pillarstructure is formed on a sidewall of the top semiconductor layer in aportion of the trench over the inner electrode. An integrated fin andstrap structure is formed by simultaneously etching the topsemiconductor layer and the epitaxial semiconductor pillar structure.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

FIG. 1A is a top-down view of a first exemplary semiconductor structureafter formation of at least one pad layer and formation of a deep trenchthrough a semiconductor-on-insulator (SOI) substrate according to anembodiment of the present disclosure.

FIG. 1B is a vertical cross-sectional view of the first exemplarysemiconductor structure along the vertical plane B-B′ of FIG. 1A.

FIG. 2A is a top-down view of the first exemplary semiconductorstructure after formation of a node dielectric layer and an innerelectrode layer in the deep trench according to an embodiment of thepresent disclosure.

FIG. 2B is a vertical cross-sectional view of the first exemplarysemiconductor structure along the vertical plane B-B′ of FIG. 2A.

FIG. 3A is a top-down view of the first exemplary semiconductorstructure after recessing the inner electrode layer and removal ofexposed portions of the node dielectric layer according to an embodimentof the present disclosure.

FIG. 3B is a vertical cross-sectional view of the first exemplarysemiconductor structure along the vertical plane B-B′ of FIG. 3A.

FIG. 4A is a top-down view of the first exemplary semiconductorstructure after formation of an epitaxial semiconductor pillar structureand a polycrystalline semiconductor material portion according to anembodiment of the present disclosure.

FIG. 4B is a vertical cross-sectional view of the first exemplarysemiconductor structure along the vertical plane B-B′ of FIG. 4A.

FIG. 5A is a top-down view of the first exemplary semiconductorstructure after recessing of the epitaxial semiconductor pillarstructure according to an embodiment of the present disclosure.

FIG. 5B is a vertical cross-sectional view of the first exemplarysemiconductor structure along the vertical plane B-B′ of FIG. 5A.

FIG. 6A is a top-down view of the first exemplary semiconductorstructure after formation of a patterned photoresist layer according toan embodiment of the present disclosure.

FIG. 6B is a vertical cross-sectional view of the first exemplarysemiconductor structure along the vertical plane B-B′ of FIG. 6A.

FIG. 7A is a top-down view of the first exemplary semiconductorstructure after formation of an integrated fin and strap structureaccording to an embodiment of the present disclosure.

FIG. 7B is a vertical cross-sectional view of the first exemplarysemiconductor structure along the vertical plane B-B′ of FIG. 7A.

FIG. 8A is a top-down view of the first exemplary semiconductorstructure after removal of at least one pad portions according to anembodiment of the present disclosure.

FIG. 8B is a vertical cross-sectional view of the first exemplarysemiconductor structure along the vertical plane B-B′ of FIG. 8A.

FIG. 9A is a top-down view of the first exemplary semiconductorstructure after formation of a gate stack structure and a gate spaceraccording to an embodiment of the present disclosure.

FIG. 9B is a vertical cross-sectional view of the first exemplarysemiconductor structure along the vertical plane B-B′ of FIG. 9A.

FIG. 10 is a top-down view of a second exemplary semiconductor structureafter formation of gate lines and gate spacers according to anembodiment of the present disclosure.

FIG. 11A is a top-down view of a third exemplary semiconductor structureafter formation of a raised source region and a raised drain region byselective deposition according to an embodiment of the presentdisclosure.

FIG. 11B is a vertical cross-sectional view of the first exemplarysemiconductor structure along the vertical plane B-B′ of FIG. 11A.

FIG. 12 is a vertical cross-sectional view of a fourth exemplarysemiconductor structure after formation of a gate stack structure and agate spacer according to an embodiment of the present disclosure.

FIG. 13 is a vertical cross-sectional view of a fifth exemplarysemiconductor structure after formation of a gate stack structure and agate spacer according to an embodiment of the present disclosure.

DETAILED DESCRIPTION

As stated above, the present disclosure relates to an epitaxial strapstructure between a fin field effect transistor (FET) and a trenchcapacitor, and a method of manufacturing the same. The aspects of thepresent disclosure are now described in detail with accompanyingfigures. It is noted that like reference numerals refer to like elementsacross different embodiments. The drawings are not necessarily drawn toscale. Ordinals are used merely to distinguish among similar elements,and different ordinals may be employed across the specification and theclaims of the instant application.

Referring to FIGS. 1A and 1B, a first exemplary semiconductor structureaccording to an embodiment of the present disclosure includes asemiconductor-on-insulator (SOI) substrate. The SOI substrate includes astack, from bottom to top, of a bottom semiconductor layer 10, a buriedinsulator layer 20, and a top semiconductor layer 30L.

The bottom semiconductor layer 10 includes a semiconductor material. Theburied insulator layer 20 includes a dielectric material such as siliconoxide, silicon nitride, a dielectric metal oxide, or a combinationthereof. The top semiconductor layer 30L includes a semiconductormaterial, which can be the same as, or different from, the semiconductormaterial of the bottom semiconductor layer 10.

Each of the bottom semiconductor layer 10 and the top semiconductorlayer 30L includes a semiconductor material independently selected fromelemental semiconductor materials (e.g., silicon, germanium, carbon, oralloys thereof), III-V semiconductor materials, or II-VI semiconductormaterials. Each semiconductor material for the bottom semiconductorlayer 10 and the top semiconductor layer 30L can be independently singlecrystalline, polycrystalline, or amorphous. In one embodiment, thebottom semiconductor layer 10 and the top semiconductor layer 30L aresingle crystalline. In one embodiment, the bottom semiconductor layer 10and the top semiconductor layer 30L include single crystalline silicon.

In one embodiment, the bottom semiconductor layer 10 can be doped withdopants of a first conductivity type. The first conductivity type can bep-type or n-type.

In one embodiment, the thickness of the top semiconductor layer 30L canbe from 5 nm to 300 nm, the thickness of the buried insulator layer 20can be from 50 nm to 1,000 nm, and the thickness of the bottomsemiconductor layer 10 can be from 50 microns to 2 mm, although lesserand greater thicknesses can also be employed for each of these layers(10, 20, 30L).

At least one pad layer can be deposited on the SOI substrate (10, 20,30L), for example, by chemical vapor deposition (CVD) or atomic layerdeposition (ALD). The at least one pad layer can include one or morelayers that can be employed as an etch mask for forming a deep trench 49in the SOI substrate (10, 20, 30L). As used herein, a “deep trench”refers to a trench that extends from a topmost surface of asemiconductor-on-insulator (SOI) substrate through a top semiconductorlayer and a buried insulator layer and partly into an underlyingsemiconductor layer.

In one embodiment, each of the at least one pad layer can include adielectric material such as silicon nitride, a dielectric metal nitride,a doped silicon undoped silicon oxide, or a dielectric metal oxide. Thetotal thickness of the at least one pad layer can be from 100 nm to2,000 nm, although lesser and greater thicknesses can also be employed.

In one embodiment, the at least one pad layer includes a stack of alower pad layer 62L and an upper pad layer 64L. The lower pad layer 62Lincludes a first dielectric material, and the upper pad layer 64Lincludes a second dielectric material that is different from the firstdielectric material. In one embodiment, the lower pad layer 62L caninclude silicon oxide, and the upper pad layer 64L can include siliconnitride. In one embodiment, the thickness of the lower pad layer 62L canbe from 10 nm to 100 nm, and the thickness of the upper pad layer 64Lcan be from 40 nm to 360 nm, although lesser and greater thicknesses canalso be employed for each of the lower pad layer 62L and the upper padlayer 64L.

A photoresist layer (not shown) can be applied over the at least one padlayer (62L, 64L) and can be lithographically patterned to form at leastone opening having an area of a deep trench 49 to be subsequentlyformed. The pattern in the photoresist layer can be transferred into theat least one pad layer (62L, 64L). Subsequently, the pattern in the atleast one pad layer (62L, 64L) can be transferred through the topsemiconductor layer 30L, the buried insulator layer 20, and an upperportion of the bottom semiconductor layer 10 by an anisotropic etch thatemploys the at least one pad layer (62L, 64L) as an etch mask. A deeptrench 49 can be formed for each opening in the at least one pad layer(62L, 64L). The photoresist can be removed by ashing, or can be consumedduring the etch process that forms the deep trench 49.

The sidewalls of the deep trench 49 can be substantially verticallycoincident among the various layers (64L, 62L, 30L, 20, 10) throughwhich the deep trench 49 extends. As used herein, sidewalls of multipleelements are “vertically coincident” if the sidewalls of the multipleelements overlap in a top-down view such as FIG. 1A. As used herein,sidewalls of multiple elements are “substantially vertically coincident”if the lateral offset of the sidewalls of the multiple elements from aperfectly vertical surface is within 5 nm. The depth of the deep trench49 as measured from the plane of the topmost surface of the SOIsubstrate (10, 20, 30L) to the bottom surface of the deep trench 49 canbe from 500 nm to 10 microns, although lesser and greater depths canalso be employed. The lateral dimensions of the deep trench 49 can belimited by the lithographic capabilities, i.e., the ability of alithographic tool to print the image of an opening on the photoresistlayer. In one embodiment, the “width,” i.e., a sidewall to sidewalldistance, of the deep trench along the direction parallel to the B-B′plane and along the direction perpendicular to the B-B′ plane can befrom 32 nm to 150 nm, although lesser dimensions can be employed withavailability of lithographic tools capable of printing smallerdimensions in the future.

Referring to FIGS. 2A and 2B, a buried plate 12 can be formed by dopinga portion of the bottom semiconductor layer 12 in proximity of sidewallsof the bottom semiconductor layer 10 within each deep trench 49. Dopantscan be introduced, for example, by outdiffusion from a dopant-includingdisposable material (such as a doped silicate glass) or by ionimplantation as known in the art. Further, any other method of forming aburied plate 12 in the bottom semiconductor layer 10 of an SOI substrate(10, 20, 30L) can be employed in lieu of outdiffusion from adopant-including disposable material or ion implantation.

In one embodiment, the buried plate 12 can be doped with dopants of asecond conductivity type which is the opposite of the first conductivitytype. For example, the first conductivity type can be p-type and thesecond conductivity type can be n-type, or vice versa. A p-n junction isformed between the remaining portion of the bottom semiconductor layer10 and the buried plate 12. The dopant concentration in the buried plate12 can be, for example, from 1.0×10¹⁸/cm³ to 2.0×10²¹/cm³, and typicallyfrom 5.0×10¹⁸/cm³ to 5.0×10¹⁹/cm³, although lesser and greater dopantconcentrations can also be employed.

A node dielectric layer 42L can be deposited conformally on allphysically exposed sidewalls in the deep trench 42L and on the topsurface of the upper pad layer 64L. The node dielectric layer 42L caninclude any dielectric material that can be employed as a nodedielectric material in a capacitor known in the art. For example, thenode dielectric layer 42L can include at least one of silicon nitrideand a dielectric metal oxide material such as high dielectric constant(high-k) gate dielectric material as known in the art.

An inner electrode layer 44L can be deposited to completely fill thedeep trench 49. The inner electrode layer 44L includes a conductivematerial, which can be a metallic material or a doped semiconductormaterial. The metallic material can be an elemental metal such as W, Ti,Ta, Cu, or Al, or an alloy of at least two elemental metals, or aconductive metallic nitride of at least one metal, or a conductivemetallic oxide of at least one metal. The doped semiconductor materialcan be a doped elemental semiconductor material, a doped compoundsemiconductor material, or an alloy thereof. The inner electrode layer44L can be deposited by physical vapor deposition (PVD), chemical vapordeposition (CVD), electroplating, electroless plating, or a combinationthereof. The inner electrode layer 44L is deposited to a thickness thatis sufficient to completely fill the deep trench 49.

Referring to FIGS. 3A and 3B, the inner electrode layer 44L can bevertically recessed to a level between the top surface of the buriedinsulator layer 20 and the bottom surface of the buried insulator layer20 by a recess etch. The recess etch of the conductive material layercan employ an anisotropic etch such as a reactive ion etch, an isotropicetch such as a wet etch, or a combination thereof. The recess etch canbe selective to the material of the node dielectric layer 42L.

An inner electrode 44 including the conductive material of the innerelectrode layer 44L is formed in the deep trench 49. The topmost surfaceof the inner electrode 44 is substantially planar, and is locatedbetween the level of the top surface of the buried insulator layer 20and the level of the bottom surface of the buried insulator layer 20. Asurface is substantially planar if the planarity of the surface islimited by microscopic variations in surface height that accompaniessemiconductor processing steps known in the art. A cavity 47 is formedabove the inner electrode 44.

The physically exposed portions of the node dielectric layer 42L can bepatterned by an etch, which can be a wet etch. For example, if the nodedielectric layer 42L includes silicon nitride, the physically exposedportions of the node dielectric layer 42L can be removed by a wet etchemploying hot phosphoric acid. The remaining portion of the nodedielectric layer 42L within the deep trench 49 constitutes a nodedielectric 42. The set of the buried plate 12, the node dielectric 42,and the inner electrode 44 constitute a trench capacitor (12, 42, 44).The buried plate 12 is an outer node of the trench capacitor, the nodedielectric 42 is the dielectric separating the outer electrode from theinner electrode, and the inner electrode 44 is the inner electrode ofthe trench capacitor. The trench capacitor is embedded within the SOIsubstrate (10, 12, 20, 30L). The buried insulator layer 20 overlies theburied plate 12 (i.e., the outer electrode).

Referring to FIGS. 4A and 4B, a semiconductor material is deposited onsemiconductor surfaces by a selective deposition process. The selectivedeposition process employs simultaneous or concurrent flow of a reactantgas and an etchant gas. The reactant gas is a precursor gas fordeposition of a semiconductor material. For example, the reactant gascan be SiH₄, SiH₂Cl₂, SiHCl₃, SiCl₄, Si₂H₆, GeH₄, Ge₂H₆, or any otherprecursor gas for depositing an elemental semiconductor material or acompound semiconductor material as known in the art. The etchant gas canbe, for example, HCl or any other etchant gas compatible withsimultaneous or concurrent flow of the reactant gas. In one embodiment,the selective deposition process can be a selective epitaxy process thatis performed at an elevated temperature that enables epitaxial alignmentof a deposited semiconductor material with an underlying semiconductormaterial.

During the selective deposition process, a semiconductor materialnucleates, and grows on, semiconductor surfaces, while the semiconductormaterial does not nucleate on, or grow from, dielectric surfaces. Thus,the semiconductor material grows from the sidewall surfaces of the topsemiconductor layer 30L. If the inner electrode 44 includes asemiconductor material such as doped polysilicon, the semiconductormaterial can grow from the top surface of the inner electrode 44.

In one embodiment, selective epitaxy of a semiconductor material can beemployed for the selective deposition process. A single crystallinesemiconductor material can grow on sidewalls of the top semiconductorlayer 30L in a portion of the trench over the inner electrode 44 to forman epitaxial semiconductor pillar structure 46′. The epitaxialsemiconductor pillar structure 46′ is formed in epitaxial alignment witha single crystalline semiconductor material of the top semiconductorlayer 30L. The epitaxial semiconductor pillar structure 46′ overlies theinner electrode 44.

In addition, a polycrystalline semiconductor material portion 45 cangrow from the inner electrode simultaneously with the growth of theepitaxial semiconductor pillar structure 46′ from the sidewalls of thetop semiconductor layer 30L. Thus, the polycrystalline semiconductormaterial portion 45 can be formed directly on the top surface of theinner electrode 44 simultaneously with formation of the epitaxialsemiconductor pillar structure 46′.

During the simultaneous growth of the epitaxial semiconductor pillarstructure 46′ and the polycrystalline semiconductor material portion 45,surfaces of the epitaxial semiconductor pillar structure 46′ come incontact with surfaces of the polycrystalline semiconductor materialportion 45 to define a boundary between the epitaxial semiconductorpillar structure 46′ and the polycrystalline semiconductor materialportion 45. As the lateral growth of the epitaxial semiconductor pillarstructure 46′ toward a center axis of the trench proceeds, the volumeinto which the growth of the polycrystalline semiconductor materialportion 45 can proceed is reduced. Once the lateral growth of theepitaxial semiconductor pillar structure 46′ reaches the center axis ofthe trench, all upper surfaces of the polycrystalline semiconductormaterial portion 45 contacts surfaces of the epitaxial semiconductorpillar structure 46′, and the epitaxial semiconductor pillar structure46′ prevents further growth of the polycrystalline semiconductormaterial portion 45.

After the growth of the polycrystalline semiconductor material portion45 stops, the epitaxial semiconductor pillar structure 46′ can continueto grow upward up to the topmost surface of the at least one pad layer(62L, 64L), and subsequently, above the topmost surface of the at leastone pad layer (62L, 64L). Crystallographic facets may be formed on theepitaxial semiconductor pillar structure 46′ above the horizontal planeof the topmost surface of the at least one pad layer (62L, 64L).

The polycrystalline semiconductor material portion 45 can be formed witha horizontal cross-sectional area that decreases with a verticaldistance from an interface between the inner electrode 44 and thepolycrystalline semiconductor material portion 45. The polycrystallinesemiconductor material portion 45 can be in contact with the top surfaceof the inner electrode 44 and a non-planar bottom surface of theepitaxial semiconductor pillar structure 46′.

The composition of the epitaxial semiconductor pillar structure 46′ maybe the same as, or may be different from, the composition of the topsemiconductor layer 30L. In one embodiment, the semiconductor materialof the epitaxial semiconductor pillar structure 46′ may be the same as,or may be different from, the semiconductor material of the topsemiconductor layer 30L. As used herein, a semiconductor material of anelement refers to the semiconductor material component of the elementexcluding electrical dopants. As used herein, electrical dopants referto p-type dopants or n-type dopants. In one embodiment, thesemiconductor material of the epitaxial semiconductor pillar structure46′ can be the same as, or may be different from, the semiconductormaterial of the top semiconductor layer 30L, and includes dopants ofdifferent types of different species than dopants of the topsemiconductor layer 30L. For example, the top semiconductor layer 30Lcan have a p-type doping and the epitaxial semiconductor pillarstructure 46′ can have an n-type doping, or vice versa. In anotherexample, the dopant species in the top semiconductor layer 30L may bethe same as, or different from, the dopant species of the epitaxialsemiconductor pillar structure 46′. In yet another example, the dopantconcentration in the top semiconductor layer 30L may be the same as, ordifferent from, the dopant concentration of the epitaxial semiconductorpillar structure 46′.

In one embodiment, the epitaxial semiconductor pillar structure 46′ andthe polycrystalline semiconductor material portion 45 can be formed within-situ doping of p-type dopants or n-type dopants. In one embodiment,the conductivity type of the epitaxial semiconductor pillar structure46′ and the polycrystalline semiconductor material portion 45 can be theopposite of the conductivity type of the top semiconductor layer 30L.For example, if the top semiconductor layer 30L has p-type doping, theepitaxial semiconductor pillar structure 46′ and the polycrystallinesemiconductor material portion 45 as n-type doping, and vice versa.

Referring to FIGS. 5A and 5B, the epitaxial semiconductor pillarstructure 46′ can be optionally recessed to optimize the height of a topsurface of an epitaxial semiconductor strap structure to be subsequentlyformed. The recessing of the epitaxial semiconductor pillar structure46′ can be performed by a recess etch. The recess etch can be ananisotropic etch or an isotropic etch, and can be selective to thedielectric material of the top portion of the at least one pad layer(62L, 64L), i.e., selective to the upper pad layer 64L. In oneembodiment, a recessed top surface of the epitaxial semiconductor pillarstructure 46′ can be between the topmost surface of the at least one padlayer (62L, 64L) and the bottommost surface of the at least one padlayer (62L, 64L). Optionally, chemical mechanical planarization (CMP)may be employed in conjunction with, or without performing, a recessetch to adjust the height of the top surface of the epitaxialsemiconductor pillar structure 46′.

Referring to FIGS. 6A and 6B, a photoresist layer 77 is applied over theat least one pad layer (62L, 64L) and the epitaxial semiconductor pillarstructure 46′, and is lithographically patterned to block an area thatstraddles an interface between the epitaxial semiconductor pillarstructure 46′ and the top semiconductor layer 30L, i.e., the sidewallsof the trench. In one embodiment, a horizontal cross-sectional shape ofthe patterned photoresist layer 77 can be a polygon having a parallelpair of lengthwise edges. As used herein, a “lengthwise” edge of apolygon refers to any edge extending along a horizontal direction thatis the same as, or is parallel to, the horizontal direction of thelongest edge of the polygon. In another embodiment, a horizontalcross-sectional shape of the patterned photoresist layer 77 can be arectangle having a parallel pair of lengthwise edges. In this case, thepatterned photoresist layer 77 can have the same width that is invariantunder translation along a lengthwise direction that is parallel to thelengthwise edges. Each of the parallel pair of lengthwise edges of thepolygon or the rectangle can straddle an interface between the epitaxialsemiconductor pillar structure 46′ and the top semiconductor layer 30L.

Referring to FIGS. 7A and 7B, the pattern in the patterned photoresistlayer 77 is transferred into the top semiconductor layer 30L and anupper portion of the epitaxial semiconductor pillar structure 46′ bysimultaneously etching the top semiconductor layer 30L and the epitaxialsemiconductor pillar structure 46′. Specifically, an integrated fin andstrap structure is formed by simultaneously etching the topsemiconductor layer 30L and the epitaxial semiconductor pillar structure46′ by an anisotropic etch. The anisotropic etch employs the patternedphotoresist layer 77 as an etch mask. The portions of the at least onepad layer (64L, 62L) and the top semiconductor layer 30L are etched bythe anisotropic etch. The anisotropic etch can employ the buriedinsulator layer 20 as an etch stop layer. A vertical stack of asemiconductor fin 30, a first pad portion 62, and a second pad portion64 can be formed by remaining portions of the at least one pad layer(64L, 62L) and the top semiconductor layer 30L.

The portion of the epitaxial semiconductor pillar structure 46′ that iscovered with the photoresist layer 77 is not recessed during theanisotropic etch. The portion of the epitaxial semiconductor pillarstructure 46′ that is not covered by the photoresist layer 77 isvertically recessed. The recessed surface of the epitaxial semiconductorpillar structure 46′ can be located between the top surface and thebottom surface of the buried insulator layer 20, or can be located abovethe top surface of the buried insulator layer 20. The remaining portionof the epitaxial semiconductor pillar structure 46′ is herein referredto as an epitaxial semiconductor strap structure 46. The photoresistlayer 77 can be removed after the anisotropic etch, for example, byashing.

The epitaxial semiconductor strap structure 46 includes a lower portion46A of the epitaxial semiconductor strap structure 46 and an upperportion 46B of the epitaxial semiconductor strap structure 46. The lowerportion 46A is located below the horizontal plane including a recessedtop surface of the epitaxial semiconductor strap structure 46, and theupper portion 46B is located above the horizontal plane including therecessed top surface of the epitaxial semiconductor strap structure 46.In one embodiment, the upper portion 46B of the epitaxial semiconductorstrap structure 46 adjoins the lower portion 46A of the epitaxialsemiconductor strap structure 46 at the horizontal plane located betweenthe top surface of the buried insulator layer 20 and the bottom surfaceof the insulator layer 20. The upper portion 46B of the epitaxialsemiconductor strap structure 40 protrudes above the top surface of theburied insulator layer 20.

In one embodiment, the upper portion 46B of the epitaxial semiconductorstrap structure 46 and the semiconductor fin 30 can have the same widththroughout. In this case, a parallel pair of sidewalls of the upperportion 46B of the epitaxial semiconductor strap structure 46 and aparallel pair of sidewalls of the semiconductor fin 30 can be within thesame pair of vertical sidewalls, and can have the same width throughout.

The entirety of the epitaxial semiconductor strap structure 46 and thesemiconductor fin 30 can be single crystalline. The epitaxialsemiconductor strap structure 46 and the semiconductor fin 30 arecollectively referred to as an integrated fin and strap structure (30,46). The integrated fin and strap structure (30, 46) can be formed witha parallel pair of lengthwise sidewalls. An end portion of each of theparallel pair of lengthwise sidewalls of the integrated fin and strapstructure (30, 46) overlies the inner electrode 44.

The first exemplary semiconductor structure of FIGS. 7A and 7B includesa trench capacitor embedded in a stack of a semiconductor substrate(i.e., the bottom semiconductor layer 10) and an insulator layer (i.e.,the buried insulator layer 20). The trench capacitor includes the innerelectrode 44, the node dielectric 42, and the outer electrode 12.

The integrated fin and strap structure (30, 46) is located on the buriedinsulator layer 20 and includes the semiconductor fin 30 and theepitaxial semiconductor strap structure 46. The epitaxial semiconductorstrap structure 46 is epitaxially aligned to the semiconductor fin 30and extends below the top surface of the buried insulator layer 20,i.e., extends below a horizontal plane including the top surface of theburied insulator layer 20.

In one embodiment, the semiconductor fin 30 and the upper portion 46B ofthe epitaxial semiconductor strap structure 46 have a same widththroughout, which is herein referred to as a fin width. Each sidewall ofthe epitaxial semiconductor strap structure 46 that defines the lateralextent of the lower portion 46A of the epitaxial semiconductor strapstructure 46 is vertically coincident with an outer sidewall of the nodedielectric 42. In one embodiment, all sidewalls of the lower portion 46Aof the epitaxial semiconductor strap structure 46 contact sidewalls ofthe buried insulator layer 20.

A vertical end wall 46E of the epitaxial semiconductor strap structure46 can be perpendicular to the parallel pair of sidewalls of thesemiconductor fin 30. The entirety of the vertical end wall of theepitaxial semiconductor strap structure 46 can overlie the innerelectrode 44. A vertical interface between the semiconductor fin 30 andthe epitaxial semiconductor strap structure 46 can be verticallycoincident with an interface between the node dielectric 42 and theouter electrode 12. As used herein, a first surface and a second surfaceare vertically coincident with each other if a vertical surface existsfrom which the first surface and the second surface do not device bymore than the sum of the surface roughness of the first surface and thesurface roughness of the second surface.

In one embodiment, a planar topmost surface of the epitaxialsemiconductor strap structure 46 can be located above a horizontal planeincluding the top surface of the semiconductor fin 30.

Referring to FIGS. 8A and 8B, the second pad portion 64 and the firstpad portion 62 can be removed by an etch that is selective to thesemiconductor materials of the semiconductor fin 30 and the epitaxialsemiconductor strap structure 46. For example, if the second pad portion64 includes silicon nitride and the first pad portion 62 includessilicon oxide, a wet etch employing hot phosphoric acid can be utilizedto etch the second pad portion 64 and a wet etch employing hydrofluoricacid can be utilized to etch the first pad portion 62.

Referring to FIGS. 9A and 9B, a fin field effect transistor can beformed on the semiconductor fin 30. The fin field effect transistor canbe employed as an access transistor of the trench capacitor (44, 42, 12)that controls flow of electrical charges into, and out of, the innerelectrode 44.

Specifically, a stack of a gate dielectric layer, a gate conductorlayer, and a gate cap dielectric layer is formed over the semiconductorfin 30 and the epitaxial semiconductor strap structure 46. A photoresistlayer is applied over the stack, and is lithographically patterned toblock an area that straddles a middle portion of the semiconductor fin30. The pattern in the photoresist layer is transferred into the stackof the gate dielectric layer, the gate conductor layer, and the gate capdielectric layer by at least one anisotropic etch. A remaining portionof the gate cap dielectric layer constitutes a gate cap dielectric 58, aremaining portion of the gate conductor layer constitutes a gateelectrode 54, and a remaining portion of the gate dielectric layerconstitutes a gate dielectric 50. The stack of the gate dielectric 50,the gate electrode 54, and the gate cap dielectric 58 collectivelyconstitutes a gate stack structure (50, 54, 58), which straddles amiddle portion of the semiconductor fin 30.

A gate spacer 56 including a dielectric material can be formed aroundthe gate stack structure (50, 54, 58), for example, by deposition of aconformal dielectric material layer and a subsequent anisotropic etchthat removes horizontal portions of the conformal dielectric materiallayer. The remaining vertical portions of the conformal dielectricmaterial layer constitute the gate spacer 56.

Electrical dopants can be implanted into portions of the semiconductorfin 30 that are not blocked by the gate stack structure (50, 54, 58),for example, by ion implantation or by plasma doping or by selectivedeposition of an in-situ doped epitaxial semiconductor material. Theimplanted portions of the semiconductor fin 30 constitute a sourceregion 30S and a drain region 30D. The portion of the semiconductor fin30 that is not implanted with the electrical dopants constitute a bodyregion 30B, which can be intrinsic or have a doping of the oppositeconductivity type as the source region 30S and the drain region 30D.

If the epitaxial semiconductor strap structure 46 and thepolycrystalline semiconductor material portion 45 are not doped prior tothe processing steps of FIGS. 9A and 9B, the electrical dopants can beimplanted into the epitaxial semiconductor strap structure 46 and thepolycrystalline semiconductor material portion 45. If the epitaxialsemiconductor strap structure 46 and the polycrystalline semiconductormaterial portion 45 are doped prior to the processing steps of FIGS. 9Aand 9B, additional electrical dopants of the same conductivity type aspreexisting electrical dopants can be introduced into the epitaxialsemiconductor strap structure 46 and the polycrystalline semiconductormaterial portion 45.

Referring to FIG. 10, a top-down view of a second exemplarysemiconductor structure illustrates implementation of the firstexemplary semiconductor structure in an array environment. Two instancesof the first exemplary semiconductor structure can be paired such thattwo drain regions 30D are integrated into a single drain region 30D, anda single semiconductor fin adjoins two epitaxial semiconductor strapstructures 46 protruding into trenches below the plane including the topsurface of the buried insulator layer 20. A unit structure including asemiconductor fin containing two source regions 30S and a drain region30D, two gate stack structure (50, 54, 58), two epitaxial semiconductorstrap structures 46, and two trench capacitors (44, 42, 12) are repeatedwithin a two-dimensional array. A lateral offset is introduced in thetwo-dimensional array such that each neighboring unit structure alongthe widthwise direction of the semiconductor fins is offset by half thelength of the unit structure along the lengthwise direction. Gate stackstructures (50, 54, 58) from neighboring unit structures are connectedto one another to form gate lines, which include active gate lineportions that straddle a semiconductor fin (30S, 30B, 30D) and passinggate line portions that contact the top surface of the buried insulatorlayer 20.

Referring to FIGS. 11A and 11B, a third exemplary semiconductorstructure can be derived from the first exemplary semiconductorstructure or the second exemplary semiconductor structure by forming araised source region 32S and a raised drain region 32D on each sourceregion 30S and on each drain region 30D, respectively. The raised sourceregion 32S and the raised drain region 32D can be formed, for example,by a selective deposition process, which deposits a semiconductormaterial on semiconductor surfaces and does not deposit thesemiconductor material on dielectric surfaces. The selective depositionprocess can be, for example, selective epitaxy. In this case, theentirety of the raised source region 32S, the raised drain region 32D,the semiconductor fin (30S, 30D, 30B), and the epitaxial semiconductorstrap structure 46 can be single crystalline with epitaxial alignmentthroughout. The raised source region 32S and the raised drain region 32Dhave a doping of the same conductivity type as the source region 30S andthe drain region 30D.

In one embodiment, the raised source region 32S and the raised drainregion 32D can be formed with in-situ doping. In one embodiment, athermal anneal can be employed to diffuse electrical dopants from theraised source region 32S and the raised drain region 32D into the sourceregion 30S and the drain region 30D, or from the source region 30S andthe drain region 30D into the raised source region 32S and the raiseddrain region 32D. In one embodiment, the raised source region 32S andthe raised drain region 32D can be formed without in-situ doping, i.e.,as intrinsic semiconductor material portions, and can be subsequentlydoped by ion implantation and/or outdiffusion of dopants from the sourceregion 30S and the drain region 30D during an anneal at an elevatedtemperature. Optionally, the electrical dopants introduced into theraised source region 32S and the raised drain region 32D by in-situdoping or by implantation may diffuse into the source region 32S and thedrain region 32D during an anneal at an elevated temperature.

Referring to FIG. 12, a fourth exemplary semiconductor can be derivedfrom the first, second, or third exemplary semiconductor structures byaltering the recess process illustrated in FIGS. 5A and 5B, and/or byaltering the anisotropic etch process illustrated in FIGS. 7A and 7B. Aplanar topmost surface of the epitaxial semiconductor strap structure 46is formed below the horizontal plane including the top surface of thesemiconductor fin 30.

Referring to FIG. 13, a fifth exemplary semiconductor can be derivedfrom the first, second, or third exemplary semiconductor structures byaltering or omitting the recess process illustrated in FIGS. 5A and 5B,and/or by altering the anisotropic etch process illustrated in FIGS. 7Aand 7B. The recessed top surface of the epitaxial semiconductor strapstructure 46 is located above the top surface of the buried insulatorlayer 20 and below the top surface of the semiconductor fin (30S, 30D,30B). The lower portion 46A of the epitaxial semiconductor strapstructure 46 contacts a sidewall of the buried insulator layer 20 andprotrudes above the top surface of the buried insulator layer 20. Theentirety of the upper portion 46B of the epitaxial semiconductor strapstructure 40 protrudes above the top surface of the buried insulatorlayer 20. The upper portion 46B of the epitaxial semiconductor strapstructure 46 adjoins the lower portion 46A of the epitaxialsemiconductor strap structure 46 at a horizontal plane located above thetop surface of the buried insulator layer 20. A planar topmost surfaceof the epitaxial semiconductor strap structure 46 may be formed below,at, or above the horizontal plane including the top surface of thesemiconductor fin 30.

While the disclosure has been described in terms of specificembodiments, it is evident in view of the foregoing description thatnumerous alternatives, modifications and variations will be apparent tothose skilled in the art. Each of an embodiments described herein can beimplemented individually or in combination with any other embodimentunless expressly stated otherwise or clearly incompatible. Accordingly,the disclosure is intended to encompass all such alternatives,modifications and variations which fall within the scope and spirit ofthe disclosure and the following claims.

What is claimed is:
 1. A method of forming a semiconductor structurecomprising: forming at least one pad layer on a top semiconductor layerof a semiconductor-on-insulator (SOI) substrate; forming a trenchextending below a bottom surface of an insulator layer within said SOIsubstrate; forming a trench capacitor comprising an inner electrode, anode dielectric, and an outer electrode in said SOI substrate; formingan epitaxial semiconductor pillar structure on a sidewall of said topsemiconductor layer in a portion of said trench over said innerelectrode; and forming an integrated fin and strap structure bysimultaneously etching said top semiconductor layer and said epitaxialsemiconductor pillar structure.
 2. The method of claim 1, wherein saidepitaxial semiconductor pillar structure is formed in epitaxialalignment with a single crystalline material of said top semiconductorlayer.
 3. The method of claim 2, wherein said epitaxial semiconductorpillar structure is formed by selective epitaxy of a semiconductormaterial.
 4. The method of claim 2, further comprising forming apolycrystalline semiconductor material portion directly on a top surfaceof said inner electrode.
 5. The method of claim 4, wherein saidpolycrystalline semiconductor material portion is formed simultaneouslywith formation of said epitaxial semiconductor pillar structure.
 6. Themethod of claim 4, wherein said polycrystalline semiconductor materialportion is formed with a horizontal cross-sectional area that decreaseswith a vertical distance from an interface between said inner electrodeand said polycrystalline semiconductor material portion.
 7. The methodof claim 1, further comprising: forming a patterned photoresist layerover said at least one pad layer and said epitaxial semiconductor pillarstructure; and transferring a pattern in said patterned photoresistlayer into said top semiconductor layer and an upper portion of saidepitaxial semiconductor pillar structure by said simultaneous etching ofsaid top semiconductor layer and said epitaxial semiconductor pillarstructure
 8. The method of claim 7, wherein said semiconductor fin andan upper portion of said epitaxial semiconductor strap structure have asame width throughout.
 9. The method of claim 1, wherein said integratedfin and strap structure is formed with a parallel pair of lengthwisesidewalls, and an end portion of each of said parallel pair oflengthwise sidewalls overlies said inner electrode.
 10. The method ofclaim 1, further comprising forming a fin field effect transistor onsaid semiconductor fin, wherein said fin field transistor is an accesstransistor of said trench capacitor that controls flow of electricalcharges into, and out of, said inner electrode.